serial: Remove unused uart_get_console

uart_get_console() has been unused since 2019's
commit bd0d9d15 ("serial: remove ks8695 driver")

Remove it, and it's associated docs.

Signed-off-by: "Dr. David Alan Gilbert" <linux@treblig.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20250608154654.73994-1-linux@treblig.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>